You could also use Reaper to host VSTs and use Rewire to route the audio back to Pro Tools. And now you can also do it with Reason as of Reason 9.5 But as was said earlier, nothing does this as elegantly as Patchwork. Plus, PW offers a number of other features that are hard to beat for VST hosting, such as chaining and layering and routing things in multiple ways. Worth every penny to buy it!